The Kerem Shalom border into the Gaza Strip, on December 13, 2013. Photo: IDF.

Israeli defense authorities announced the seizure of “several bulletproof plates” at the Kerem Shalom crossing between Israel and the Gaza Strip, Israeli trade news website Port2Port reported on Sunday.

Officials said it was the first time the authorities at Kerem Shalom have discovered the bulletproof sheets making there way into Gaza, according to the report. They were likely destined to be used to reinforce military installations in the Gaza Strip.

Israeli military and customs officials have apparently launched a probe into the illegal import, especially as officials said it remained unknown which group was trying to smuggle such material into Gaza.

Border officers’ discovered the plates in a truck transporting spare car parts, Port2Port reported according to a statement.

Israeli defense officials recently noted that Hamas and other terrorist groups in Gaza have continued to develop their rocket and missile arsenals since the end of the 2014 summer war between Hamas and Israel.

Defense officials also indicated that Hamas has stepped up its tunnel-building operations, after the IDF destroyed dozens of of such tunnels during the 2014 conflict.

Israeli maintains a land, air and see blockade on the Gaza Strip.